Mixing



April 28, 1942. cH s 2,281,477

MAGNES'IA REFRACTORY Filed Sept. 15, 1937 DOLOMITE OR SEA WATER ORDOLOM'T'Q OTHER BRINE. LIMESTONE CALCINED & MODIIZTYING SLAKEDTO FORM lwe A SLURRY. M X lMPURlTlEs I I I SETTLING t I I I I CONCENTRATING I I II WASHING F DRYING CALCINING GRINDING I GRADING 8:

MIXING MOULDING Jnuenfox' F|R|NG jWMrY/M Patented Apr. 28, 1942 UNITEDSTATES MAGNESIA' REFRACTORY I Heinz Henry Chesny,

Worksop, Nottinghamsh ire, England I Application September 15,1937,Serial No. 164,088: r In Great Britain September 24, 1936 14 Claims.

This invention is for improvements inor relating tomagnesiarefractories. High temperature refractories are produced at present bycalcining the mineral magnesite, native MgCOc, at temperatures ,rangingfrom 1350 C. to 1800 C. r 'fiintered magnesite clinker thus producedconessentially of spherical particles.

high-grade Austrian magnesite approximately 13% of impurities includingiron oxide, silicates.

alumina and the like, and thus there is generally sufiicient bondingmaterial present to bring about a cementing together of the particles.In the case of a chemically purer magnesite such as Grecian m'agnesite,iron oxide or other fluxforming impurities are added to form the glassybond. The presence of these impurities causes the formation of compoundspossessing relatively low melting points and as a consequence, asoftening of the bond occurs causing a slippage of magnesia particles.Ultimately collapse of the brick takes place under conditions of hightemperature and load.

The use'of native magnesite does not permit of the use of the mostadvantageous composition of bonding material. due to the fact that theimpurities initially present in the mineral cannot be altered, except bythe addition of further amounts of impurities. Obviously, the mostadvantageous composition of amagnesia refractory would be that at whichthe bonding material is proportioned in such a manner as to permit asintering just below the maximum tern:

' without a glassy bond,- if the-material consistedof-. the usualspherical particles. The magnesia clinker producedfrom magnesiumhydroxide pre pared as described above is obtained, however,

V in the form of needle-like fragments.

The present invention accordingly comprises Native magnesite a processfor the. manufacture. of, a refractory.

is relatively impure and contains in the case of sea water'or brinecontaining magnesium. ch10 ride or magnesiumv sulphate or both. i A

The product madev in accordance with 'the above-mentioned specificationpossesses the ad:-

vantage .of exceptionally; high chemicalkpurity, it v and issubstantially free from low melting point; impurities. As aconsequencait would-be dife ficult to obtain a cementing of the magnesiamaterial consisting of elongated particlesgwhich includes the step ofpreparing magnesium hy-.

. droxide by the treatment of sea water ora brine Y containingconvertible magnesiumsalts with calfcined dolomite or ;dolo'mticlimestone The sea water or brine maybetreated with anaqueous slakeddolomite or dole} slurry. of calcined and mitic limestone.

The invention furthercomprises a process its." the manufacture of deadburnt magnesia in the form of elongated fragments and suitable 'for usein the production of refractoriesj'whic'h' comprises treating a brinecontaining: convertible magnesium salts with an aqueous slurry ofcalcined and subjecting it to calcination to form a clinker.

perature at which the refractory is burned due allowance being made alsofor the presence of other substances, such as chromium compounds.

added for the purpose of preventing spalling of the refractory.

I have found that brines containing convertible The precipitatedmagnesium hydroxide may be purified e. g. by'washingpriorto dryingand'cal- 1 v cinatiom '1 Coarsecrushingqot @theinitial clinker producesfragments measuring on anaverage 4 mm. ,in I length. and 0.5 mm. inWidth-=Y.The finegrinding of the clinker causes its disintegration toitsultimate aggregate size,-ranging between 10 microns and -emicrons, theaveragebeingaboutw50 the fragments being elongated in microns, allshape.

The mechanical interlacing of boththe'finely -ground andthecoarsely'crushed elon'gatedpar 'ticles fo'rms a particularly strongstructure, even in the absenceof low melting glass. AS a confsequence,an exceptionally high refractoriness' under load isobtained, and at thesame time the bricks made from the product do notspall under conditionsof varying "temperature,

As an added advantage, the elongated par-Q ticles are especially usefulfor iettling, 1e. vg. re pairingthe refractories inv steelfurnaces, asthe ATENT 0mm elongated shape of the-material causes a particularly goodadherence.

In certain cases it is thus unnecessary to add any impuritiesconstituting a bond but in order that any such substances added to themagnesium hydroxide for the purpose of modifying the properties of theclinker may be distributed intimately and; uniformly throughout theprecipi- J,

tated magnesium .-hy.droxid the said impurities may be introduced intothe brine and/or into the slurry. Alternatively, the impurities -may beintroduced: during or immediately after, the;

formation of the magnesium hydroxide; -If the modifying substance isadded to the brine .before' the addition of the slurry, an advantage isthat clinkermay be used as such, or it may be crushed,

sieved and graded. The graded material may be re-mixed in the properproportions of coarse, medium and finegrains, the mixture pressed intothe desired shape by first wetting it with water, dried and burned'at atemperature suiiicient to cause proper bonding.

The resulting refractory *material possesses properties superiorto thoseof refractory material produced from magnesite. Thus, refractory=m'aterial produced by use of the present invention possesses low.porosity, high specific gravity,

the added modifying substancebecomes incorporated in the crystals of,magnesiumhydroxide,

as they are formed.

The magnesium hydroxide precipitate is con-' cen'trated, washed,filtered, dried and calcined and if desired any-added impuritiesmodifying the properties of'the clinker may be introduced in liquidwith; which the magnesium hydroxide is washed prior to: dryingandcalcinatio'n; Modifying impuritiesmay include substances such' ascompounds of "calcium, silicon or iron forming with magnesia compoundsof lower melting point or substances such as compounds of 'ohromium orzirconium minimizing; spalling in the final rei'ractory' material: Someof these materials may conveniently be'in the form of a solution.

In certain cases it has been found desirable to incorporate in amagnesium oxide refractory a proportion'of iron'oxide in orderto formabond between the particles of the magnesium oxide and in such cases ithas been found that by adding an iron solution, e. g. ferricchloridesolution,

" exceptionally high resistance to temperature under loadand highresistance to attack by slag. A further special'advantage of themagnesia produced in accordance with the present invention isthatdea'dbuming may be brought about readily, as the decompositiontemperature of the magnesium hydroxide is only a fraction of that of themagnesite ordinarily used.

Following is a description by way of example of methods of carrying theinvention into effect a Example I Magnesium hydroxide isprecipitatedfrom treated sea water and a slurry derivedfrom calcined impure dolomitein accordance with theprocess. described in copending applicationSerial,

No. 164,087, now Patent No; 2,224,780. The precipitatedmagnesiumhydroxide is concentrated;

to so to 40% solids and is then-washed, dried,

and" calcined. Thelcalcined product which is in to the sea water themagnesium oxide finally 05- V tained will conta-inderric oxide'uniformlydistributed throughout the mass' It has further,

been-found that the addition of an iron salt such as ferric chloridebrings about an increased rate of settling of the precipitate ofmagnesium and/or calcined. i

It is often advantageous to introduce dried or partially dried materialinto the retort or kiln in which it is to be finally calcined in theform'of small pieces, e. g; of regular shape. pieces may be" formed on awire beltor may be produced by a moulding or like process. Thus they may7 be produced by drying the "slurry on a belt provided'withcorrugationsor indentations and arranged to -pass through a'tunneldrier; This method of treatment has the additional advanplying a coatingof the wet precipitate-to a sur- .centrated -to 30-to 40% solids and isthen dried tags that dusting of the dried product is reduced.

The drying of the magnesium hydroxidemay', al-v ternatively be carriedout by applying a coating of the wet precipitate to a surfaceonwhich itis subsequently dried.

'Calcination is carried out .at. above 1300 C. in order to shrink anddead burn the magnesia and in the final heating stage of the process itis preferable to employ a temperature of l600 C; or over. Heat ispreferably applied gradually during the initial steps of removing thefree and combinedwater. The resultant a temperature the form of anagglomeration of ticleshas the composition;

Per cent This material, whenre-calcined, for only one,

hour at 'a temperature of 1550" C. in the form of a brick, withstood atemperature'of over 1700 C.-

under a load of fifty pounds per square inch without collapsing.

The magnesium hydroxide may be dried by apface on which it issubsequently heated or'it may beintroduced directly into a rotary kilnand fired in order to drive off first the free water and then i thecombined water, the magnesium oxide thus -formed beingheated further toa temperature above 1300? C. to shrink it and to render it inert. Thefinal step ofthe heating may be; carried out at a temperature of 1600 C.or over.

Example II i a A relatively pure dolomite is-calcined, 'slaked andtreated by the process described in Example I, the precipitatedmagnesium hydroxide being subsequently concentrated. washed, dried andcalcined. The artificial magnesium oxidethus.

produced was in the form of an agglomeration of clongated particles andhad a composition as folowsz.

- Per cent MgO 97.5 CaO -i 1.2 SiOz 0.8 R203 -0.5 Alkalies Trace Example1!! There is added to the sea water emplogdfor elongated pardescribedin- Example Ii a proportion of fer'ric 1" chloride solutionobtainedbythe additon of softened se'a waterto mill scale. the amount orferric chloride. solution being .such as to yield 2.5 FezOa in themagnesium oxide refractory-finally produced.

The softening of thesea water by the removal of calcium therefrom andthe precipitation of the magnesium hydroxide and its subsequentcalcination to form dead burnt; magnesium oxide are carried out asdescribed in Example 1. Alternatively, the magnesium hydroxide slurrymaybe converted to magnesium oxide by drying and calcining the slurry whilepasted into the meshes of a wire belt, the calcined material beingremoved from the belt by tapping. v

In an alternative method of preparing a high temperature magnesiarefractory containing a relatively small proportion of a substance suchas iron oxide which forms a bond between the elongated particles of thedead burnt magnesium oxide, a solution of the material to be added, e.g. ferric chloride may be mixed with the liquid with which the magnesiumhydroxide slurry. is washed immediately prior to drying and calcination.

Example IV In the production of a refractory magnesia brick from clinkerprepared as described in the preceding examples the clinker is crushed,sieved and graded. The graded material is re-mixed in the properproportions of coarse, medium and The mixture is moulded into thedesired shape, preferably by first wetting it with water, to which aproportion of binder may be added, and is dried and burned at atemperature sufllcient tov cause proper binding. The resulting brick hasa high specific gravity, low porosity and high resistance to attack byslag and to deformation under load at high temperatures.

The accompanying diagrammatic drawing illustrates one embodiment of thepresent process in which a slurry of calcined and slaked dolomite ordolomitic lime is mixed with sea water and the precipitate of magnesiumhydroxide is concentrated, washed, dried and calcined. The calcinedproduct may be ground. graded, mixed. if desired with other materials,moulded into the form of the refractory article to be produced andfired.

Modifying impurities; if added, may be introduced when the dolomiticslurry is being mixed with the sea water or at the settling or washingstages.

I claim.

1. A dead burnt magnesium oxide clinker consisting of agglomerates oflong and relatively thin particles. v an 2. A ground dead burntmagnesium oxide clinker the coarsely 'crushed particles whereof average4 mm. in length and 0.5 mm. in thickness and the finely ground fractionwhereof contains elpngate'd particles ranging between microns and 120microns in length.

3. A- synthetic dead burnt magnesium .oxide clinker consisting ofagglomerates of elongated particles the length of the coarsely crushedparame? the recipitation 1magnesi um l hydroxide min;

ticles whereof variesbetween s and- 12 times tniri' the;slurry.derived-from a calcined 'dolorni te' as e dianieterczn;

- 4.1A synthetic dead burnt magnesium -oxide clinker. consisting of:ultimate particles 30 to 7055 microns; in length and? agglomeratedto'fo'rm needle-like fragments-over 1 mm. in leng'tli'. l' 5. A's-moldedand. burntrefractory article on-- sisting of a moulded mixturecontaining crushed and graded dead burnt magnesium oxide clinker in the'form'of long and relatively thin pa'rticlesQ- 6. Dead burnt magnesiumoxide-clinker in the form of elongated particles; the? lengths brwnieh'tare many times the diametersthereojf. 7. A process for the manufactureof a granu= lar refractory material comprising elongated par! ticles ofdead burnt magnesia which includes the steps of preparing crystallinemagnesium in:

droxide by the treatment of a brine having sub stantially the propertyof sea water of containing convertible magnesium salts with a slurry ofcal ,cined dolomite or dolomitic limestone and dead burning thecrystalline magnesium hydroxide so prepared.

8. A process for the manufacture ofa granular refractory materialcomprising dead burnt magnesia in the form of agglomerates of elonigated fragm ts which includes the steps of preparing cry tallinemagnesium hydroxide by the interaction. of an aqueous solution havinggether a brine having the characteristic property of sea water ofcontaining convertible mag nesium salts and an aqueous slurry ofcalcined and slaked dolomite or dolomitic limestone, separating off theprecipitated crystalline magnesium hydroxide so formed and dead burningthe magnesium hydroxide to forma clinker.

10. A process as claimed in claim 9wherein the crystalline magnesiumhydroxide is washed free from soluble impuritiesprior to being subjectedto dead burning to form a clinker of magnesia.

11. The herein described process for the mann facture of a refractorymaterial comprising dead burnt magnesia in the form of elongatedparticles which process comprises reacting a brine.

having substantially the property of sea water of containing convertiblemagnesium salts and an aqueous slurry of calcined and slaked dolomite ordolomitic limestone to form crystalline magnesiumhydroxide, separatingon the said crystalline magnesium hydroxide, concentrating the saidcrystalline magnesium hydroxide to form" a pastymass containing between28% and 40% solids and subjecting the said mass to dead burning in arotary kiln to form a clinker.

12. The herein described process for the manufacture of a granularrefractory material comprising dead burnt magnesia in the form ofelongated particles which process comprises reacting together a brinehaving the characteristic property of sea water of containingconvertible magnesium salts and an aqueous slurry of calcined and slakeddolomite or dolomitic limestone to form a precipitate of crystallinemagnesium hydroxide from the liquid, drying it in the form of relatively'small pieces and dead burning said smallpieces to form aclinker. v

13. A process for the manufacture of dead burnt magnesia in the form ofelongated particles which comprises calcining dolomite to convertsubstantially all the carbonate to oxide, forming a slurry ofthecalcined dolomite, mix ing the slurry with a brine having the propertyof sea water of containingconvertible magne sium salts in a vessel towhich the brine is admitted so as to impart to the body of liquid agentle rotary or swirling motion, introducing the slurry below thesurface of the brine so as to prevent or minimize the formation 01'hydrous magnesium hydroxide, separating the preclpitated crystallinemagnesium hydroxide from the" liquid, drying the crystalline magnesiumhydrox ide thereafter dead burning it to forms clinker. 14. A process asclaimed in'iclai'm 9 in which the precipitated crystalline magnesiumhydroxide'is concentrated to approximately 30% or 40% solids priorto'the dead burning thereof and in which the dead burning is carried outat a temperature of above 1300 C.

i v HEINZ HENRY CHESNY;

